This invention relates to roller chain and sprocket drives.
Roller chain and sprocket drives are commonly used for transmitting torque from one shaft to another, for example for driving the camshafts of an internal combustion engine from the crankshaft. Such drive systems may be prone to undesirable levels of noise or wear.
When a roller in a roller chain engages with a sprocket tooth an impact occurs. This impact is caused by the geometry of the drive and also by manufacturing tolerances on the chain and the sprocket. The impact may be considered to have two components, one perpendicular to the span of chain from which the roller is being picked up, and one along the chain. It is the component along the chain span which is the cause of much of the high frequency noise from a roller chain drive. The perpendicular component of the impact is generally of smaller magnitude and not as significant as a noise source. In addition to causing noise, the impacts increase the loading on the chain and the sprockets, so reducing the fatigue life of the chain.
Thus each time a sprocket tooth picks up a roller from a chain span, noise and vibration are excited. Only a few of the sprocket teeth, those nearest the end of the span from which the sprocket is picking up rollers, are active in carrying the load and transmitting it between the sprocket and the chain.
It is known from FR 572 312 A (DRANCÉ) to provide a sprocket with tooth spacing that is a multiple of the pitch of the chain.
The invention seeks to provide an improved roller chain and sprocket drive that is capable of reducing noise or wear level in certain applications.
According to the invention, a roller chain and sprocket drive system comprises:
a roller chain having multiple rollers arranged with a substantially constant pitch and connected by articulated links;
a sprocket in driving or driven engagement with the roller chain, the sprocket having angularly spaced teeth arranged for driving or driven engagement with the rollers;
the spacing between at least some adjacent teeth is a multiple of the pitch of the chain rollers so that during each rotation of the sprocket at least some of the chain rollers passing over the sprocket have no driving or driven connection with the sprocket;
the sprocket is formed with a support profile (23) between adjacent driving/driven teeth; and
the support profile follows an arc centred on the sprocket axis and of radius substantially equal to the root radius of the sprocket teeth CHARACTERISED IN THAT
the support profiles are provided by resilient inserts;
the resilient inserts extend towards the sprocket axis between spoke portions;
the driving/driven teeth are formed at the outer end of spoke portions; and
the spoke portions flex tangentially under load sufficiently to accommodate variations in the distance between adjacent rollers from the average pitch.
The design of a sprocket according to the present invention intended for use with any given roller chain has fewer teeth than a conventional sprocket so that some rollers do not engage on a tooth. The number of impacts which occur, and have components along the chain, are thus significantly reduced and the effects of the components of the impacts which are perpendicular to the chain span can be reduced. The invention provides additional flexibility at the tooth and thereby provides cushioning of longitudinal impacts as the rollers engage with the sprocket teeth. The invention may also provide improved distribution of forces between the teeth in engagement with the span of chain around the sprocket by accommodating tolerances in the sprocket and the chain. The invention will provide quieter chain drives and will also improve the fatigue life of the chain. The design is such that the relative rotation of the rollers on their bearings will also be reduced, so reducing the work done against friction and increasing the drive efficiency. The invention can be applied to all roller chain drives and in particular to high speed drives such as camshaft drives in internal combustion engines.